The primary objectives of the proposed research are (1) to investigate the speech processing abilities of the young infant between the ages of two and eight months, (2) to delineate further the operating characteristics and tuning functions of the detector systems presumed to underlie the perception of speech at the phonetic level, and (3) to trace the developmental course of speech processing in young school-aged children and to relate this form of competence to the development of reading. Specific studies are designed to provide information on possible biologic and experiential influences on the development of speech processing and the mechanisms that serve this function as well as provide information necessary for the construction of theoretical descriptions of speech processing and the role that speech processing plays in the attainment of higher-order linguistic functions. The methodologies will vary with the subject population and the problem to be investigated. Studies with young infants will use a high amplitude sucking (HAS) procedure, whereas studies with older infants will use a visually reinforced head turning procedure. Investigations of detector systems will use adult listeners and a selective adaptation procedure. Investigations with school-aged children will use a variety of procedures, such as psychophysical methods to obtain identification and discrimination functions, same-different reaction time methods, and short-term recall methods that permit assessment of the underlying memory code.